1. Field of the Invention
The present invention relates to the oxidation of ethylbenzene to form products comprised of ethylbenzene hydroperoxide and acetophenone. In particular, the invention provides a method for increasing the amount of acetophenone which is formed relative to ethylbenzene hydroperoxide by reducing the alkali metal content of the ethylbenzene oxidation reaction mixture to below 0.1 ppm and by incorporating small amounts of water in the reaction mixture.
2. Description of the Prior Art
The oxidation of ethylbenzene to form products comprised of ethylbenze hydroperoxide is a known reaction which is practiced commercially in the coproduction of propylene oxide and styrene monomer. Ethylbenzene hyroperoxide thus formed is reacted with propylene to form propylene oxide with the hydroperoxide mainly being converted to methyl benzyl alcohol; some acetophenone is formed in this step as well as in the ethylbenzene oxidation step. Generally, the acetophenone is hydrogenated to methyl benzyl alcohol and such methyl benzyl alcohol, together with that formed by reaction of the hydroperoxide with the olefin, is dehydrated to the styrene monomer coproduct. U.S. Pat. No. 3,351,635 is illustrative of this technology.
U.S. Pat. No. 3,439,001 teaches that recycle ethylbenzene in the above process is advantageously treated with alkali in order to avoid residue formation during the propylene epoxidation. The treated ethylbenzene is desirably washed to remove residual alkali.
U.S. Pat. No. 4,066,706 provides a method for oxidizing ethylbenzene to the hydroperoxide whereby temperature of reaction is decreased in the direction of flow.
U.S. Pat. No. 2,867,666 teaches the oxidation of ethylbenzene to ethylbenzene hydroperoxide and stresses that the reaction should be carried out under anhydrous conditions and that the presence of basic material is critical.
U.S. Pat. No. 2,592,857 takes issue with the above and provides data (Table III) showing that acetophenone make increases and ethylbenzene hydroperoxide make decreases with the addition of increasing amounts of alkali.
Japanese patent publication 43-14449 which is by the same inventor as U.S. Pat. No. 3,592,857, carries out ethylbenzene oxidation to ethylbenzene hydroperoxide in the presence of small amounts of water, i.e., 0.5 to 2% by weight. Runs both with and without added alkali are described. Alkali is described as useful in preventing acids which are formed during oxidation from acting to decompose hydroperoxide or from inhibiting oxidation. The data suggest that water addition decreases ethylbenzene oxidation rate.
U.S. Pat. No. 4,262,143 describes the preparation of ethylbenzene hydroperoxide by oxidizing ethylbenzene in the presence of small but critical amounts of sodium or potassium hydroxide or salt, i.e., 0.1 to 20 ppm of sodium or 0.17 to 34 ppm of potassium whereby rates and selectivities to the hydroperoxide are improved.
During practice of the process for the co-production of propylene oxide and styrene monomer, frequently it is advantageous to be able to quickly and conveniently vary the ratio of the main products in accordance with market variations. The present invention provides a method whereby this variation can be accomplished without the necessity for severe changes in processing procedures and without the necessity for major capital equipment changes.